Known in the prior art is an apparatus for manufacturing corrugated tubes comprising tools, a unit for clamping and sealing the tubular billet, a forming liquid delivery unit and a unit for creating an axial compression force. The apparatus incorporates a means for controlling the pressure of the forming liquid and a means for controlling the amount of the forming liquid to suit the axial compression force (see U.S. Pat. No. 2,919,740).
However, said control of the pressure of the forming liquid and of the axial compression force causes a biaxial stressed state in the material of the tubular billet which results, as a rule in a, considerable thinning out of the corrugation apices and, as a consequence, in low operating characteristics of the product.
Also known in the prior art is an apparatus for manufacturing corrugated tubes comprising tools, a unit for clamping and sealing the tubular billet, a unit delivering the forming liquid and an axial compression unit. In this apparatus, the pressure of the forming liquid is raised until the wall of the tubular billet is bent to a certain degree under the effect of the pressure of the forming liquid delivered into the tubular billet. Then the tubular billet is subjected to an axial compression load while the pressure of the forming liquid is kept constant to the point when the corrugations are fully formed see U.K. Pat. No. 641,389, granted in 1950).
However, the material of the tubular billet in the prior art apparatus is subjected to biaxial extension which usually adversely affects the quality of the finished product.
Known in the prior art is an apparatus for manufacturing corrugated tubes comprising a bed which mounts a unit with a hydraulic drive for clamping and sealing a tubular billet, a device for axial compression of the tubular billet, holders with appropriate tools, and a device for delivering pressurized liquid into the tubular billet.
The clamping and sealing unit is designed to orient and clamp the tubular billet relative to the tools and, additionally, to prevent the forming liquid from leaking out of the tubular billet, said liquid being delivered under pressure into the tubular billet.
The clamping and sealing unit is fixed on the bed and comprises two coaxial movable members. These members are mounted at a certain distance from each other for locating the tubular billet between their ends. The members are installed in bodies rigidly fixed on the bed and are capable of moving relative to the bodies towards each other for clamping and sealing the tubular billet. In the course of tube forming the ends of the members fit tightly against the ends of the tubular billet, reliably sealing the inside space of said billet.
The axial compression device is intended to produce a compressing force applied axially to the tubular billet. Inasmuch as the length of the tubular billet diminishes in the process of forming, the device ensures convergence of the movable members of the clamping and sealing unit for maintaining a constant contact between the ends of the members and the tubular billet and ensures hermetically sealing of the billet space which is supplied with the forming liquid.
The axial compression device consists of a bed-mounted hydraulic cylinder whose rod is rigidly connected with the frame which has tapered side surfaces. These surfaces interact with the ends of two-arm levers arranged symmetrically to the axis of the hydraulic cylinder. The lever axles are fixed on the bed of the apparatus. The other ends of the levers are kinematically coupled with the movable members of the clamping and sealing unit. During the movement of the hydraulic cylinder piston, the piston rod moves the frame with the tapered side surfaces. These surfaces press the ends of the two-arm levers. The levers turn about their axes, the other ends of the levers press the members towards each other and thus clamp the tubular billet located between the members.
The tools installed on the holders are intended to fit around the tubular billet so that in the course of forming the corrugations by the pressure fed into the billet, the latter would take the shape corresponding to the shape of the tool.
The holders with tools are mounted with a provision for moving relative to each other in a plane which is perpendicular to the axis of the tubular billet. The tools are moved by a hydraulic cylinder whose rod is connected with the holder and its body, with the bed of the apparatus. After the tubular billet has been clamped between the members, the holders with tools are actuated by the pressure supplied from the cylinder, and the tools encompass the tubular billet.
The device for delivering pressurized liquid is intended to supply this liquid into the tubular billet for making corrugations thereon.
The device for delivering the forming liquid comprises a liquid source which is supplied under pressure by a pump communicating via a hydraulic intensifier with the inside space of the tubular billet. In this space, the forming liquid flows through an appropriate axial through channel in one of the movable members. The hydraulic intensifier is designed to step up the liquid pressure in the hydraulic drive, said liquid being delivered by a motor-driven liquid pump.
The device for delivering the forming liquid comprises also a pressure regulator connected parallel to the pump and serving to control the pressure of the forming liquid delivered into the tubular billet. After starting the pump, the liquid of the hydraulic drive enters the intensifier after which it flows under a higher pressure into the space of the tubular billet. The air is expelled from the tubular billet through a channel in the clamp. After expulsion of the air this channel is closed by a special valve (see, for example, U.S. Pat. No. 2,654,785).
The prior art apparatus for manufacturing corrugated tubes has a provision for controlling the pressure of the forming liquid delivered into the tubular billet. However, the prior art apparatus has no means for controlling the force of axial compression of the tubular billet in the course of forming corrugations on the tubular billet.
By theoretical research of the process of manufacturing corrugated tubes it has been established that this process requires controlling both the pressure of the forming liquid inside the billet, and the axial compression force.
The joint control of the pressure of the forming liquid delivered into the tubular billet and of the force of axial compression is required for building up a uniaxial stressed state in the material of the tubular billet which, as it has been found, is most advantageous for obtaining the geometrical parameters of the tubes with corrugations ensuring their best operationg qualities such as cyclic strength, durability and stiffness.
It is necessary that changes in the pressure of the forming liquid delivered into the tubular billet are synchronized with the changes in the force of axial compression so that there should be an adequate relationship between these controllable parameters ensuring a uniaxial stressed state.
The prior art apparatus fails to ensure joint control of the pressure of the forming liquid and of the force of axial compression which usually results in an inferior quality of corrugated tubes from the standpoint of the above-mentioned consumer characteristics.